On axles of a motor vehicle, e.g. front axle multi-link axles, torsional and cardanic movements generated by steering and spring movements in a spring strut representing a connecting element between the axle and the body of the vehicle are transmitted. The spring strut must therefore be designed to absorb these disturbing movements without damage to the component elements of the spring strut. As a rule, therefore, a spring strut has flexible component elements, e.g. an air spring bellows, preferably embodied as a tubular rolling bellows.
In previous embodiments of an air spring, use is made of an air spring bellows which has a small number of layers of textile reinforcements and is configured as an externally guided variant. In spring strut embodiments which are now customary, the air spring bellows generally has two layers of textile reinforcements, in which the respective reinforcing threads are arranged crosswise at a defined angle, e.g. 70°, to the central longitudinal axis of the spring strut. To compensate for the torsional stiffness to which this gives rise, the air bellows of current spring struts often additionally have a cardanic fold, wherein this exposed region between an air spring cover and the outer guide of the spring strut is reinforced by additional textile and/or elastomer layers laid crosswise. The air spring bellows of known spring struts are of basically continuous construction from the air spring cover to the piston clamping location on the rolling piston side.
As a rule, therefore, known embodiments of the spring struts are generally torsionally stiff. This means that they can absorb torsional movements only to a limited extent in the region of a rolling and/or cardanic fold. Relatively large torsional loads thus lead to premature failure of the air spring bellows in the region of the rolling folds.
To reduce the torsional stiffness of the spring struts, use is made in the prior art of air spring bellows designs in which the reinforcing threads of the textile reinforcements preferably extend approximately parallel to the central longitudinal axis of the spring struts. However, to meet the conflicting requirements in respect of comfort, air spring bellows of this kind are generally embodied with textile reinforcements in just one layer. Satisfying the requirements in respect of comfort and reducing torsional stiffness represent conflicting aims, entailing methods of construction for the air spring bellows which differ and which have hitherto not been achievable in any air spring bellows of unitary construction.
Publications EP 1 285 181 B1 and DE 100 09 912 C1, both incorporated by reference, represent the prior art in respect of the air spring assembly.